The present invention relates generally to improvements in cameras with flash devices in which there are provided two or more interchangeable objective lenses of different focal lengths which are selectively alternatively transferrable to an operable position registering with the camera picture taking axis.
In a camera having two or more objective lenses of different focal lengths, the picture-taking range, namely, the angle of view of the picture-taking optical system, is dependent on the lens selected. For example, in a camera in which a standard lens and a telephoto lens of longer focal length than that of the standard lens are incorporated as objective lenses, if the telephoto lens is selected, a narrow angle of view is effected, as compared with the case where the standard lens is selected. Where it is desired to take a picture of an object by using a flash device, for example, by illuminating an object by means of an electronic flash device, it is customary to incorporate in the camera a flash device which has an illuminating or irradiating angle coincident with the angle of view of the lens having the shortest focal length (the standard lens in the above-described camera). With such a camera, if a lens having a longer focal length (the telephoto lens in the abovedescribed camera) is selected, only part of an irradiating angle of the flash device is consequently utilized, because of the telephoto lens having a narrow angle of view, as compared with that of the standard lens. In other words, with telephotography, an area beyond the angle of view of the telephoto lens is irradiated by the flash device, and a loss of the energy of the irradiated light results with the resulting inefficiency, restriction and other drawbacks.
In a camera equipped with two or more selectively operable lenses having different focal lengths, it is customery that, the lens with the longest focal length has an F-number greater than those of the other lenses. For among other reasons, there is the requirement to reduce the size of the lenses in order to house these lenses in the confined space within a camera body. However, if the lens of longer focal length is given the same F-number as that of the lens of a shorter focal length, the overall size of the long focal length lens must be larger than that of a lens having the shorter focal length. As a result, such lens cannot be housed in the camera without increasing the overall size of the camera body. In terms of the constant luminosity per unit quantity of light from the flash device, a difference in possible flash-photographic camera to object distance arises between these two lenses, and due to the fact that the F-number increases, with an increase in focal length, short distance photography alone is possible. From the viewpoint of proper functioning of the camera, it is necessary in the camera that, for an object standing at a normal distance from the camera (for example, an object at a distance of 3.5 m from the camera), the flash-photography be achieved at a proper exposure level, even if any lens is selected. To meet the above requirements, the luminosity per unit quantity of light from the flash device must be set to a value at which the object at the aforesaid distance from the camera be flash photographed at a proper exposure level, when the lens having the greatest focal length, (the telephoto lens in the aforesaid example) is used. Thus, a flash device to be incorporated in a camera is bound to increase its guide number as well as its size to a greater extent, resulting in an increase in the overall size of the camera body.